Diamonds 101: Carat vs Karat

Carat vs karat: what's the difference?


In this paper, we'll explain the differences between carat and karat, two terms which carry different meanings and are often confused.

In brief, carat is a unit of weight used for diamonds and other gemstones, whereas karat is a unit of purity used for gold.


A carat is a metric unit of weight used to measure precious gemstones, particularly diamonds.

One carat equals 200mg (or a fifth of a gram), so a diamond weighing one gram would be five carats. If the weight is below one carat, the measurement referred to as either a fraction (such as a quarter, half or eighth of a carat) or as a decimal (for example, 0.50ct).

Carat is one of the 'four Cs' used to determine the quality of a diamond. The others are cut, clarity and color. The most valued diamonds are those that have good clarity and are colorless, but size does make a difference.

The history of the term dates back to ancient times, when traders used carob seeds on balance scales to determine the weight of gemstones. As time passed, the world evolved into carat and an exact weight was assigned.


Karat is a term used to indicate gold purity. It's based on the percentage of gold compared to alloy in a piece of gold.

Pure gold is 24-karat, but because gold is a very soft metal it is not able to used practically as jewelry in its purest form.

As such, it is normally mixed with metal alloys which vary depending on the gold colour. Yellow gold alloy is a mix of copper (40% to 75%), zinc (1 to 15%) and pure sterling (10 to 60%), with traces of a de-oxidant such as silicon dioxide or boron. White gold alloy is a mix of copper (around 40%) , nickel (around 40%), zinc (from 10 to 20%), sterling (from 5 to 10% ), with a trace of de-oxidant. There are also alloy mixes with palladium instead of nickel, which has become more popular recently as nickel-free jewelry has become more widely available on the market, even in high-end jewelry.

Each karat indicates 1/24th of the whole, so if a piece of jewelry is made of metal that is 18 parts gold and six parts copper, it is 18-karat gold.

The karat is normally responsible for determining the relative value of a piece of gold. In most cases, 10k is lowest purity that can still be considered gold and 18k is the highest purity commonly available, but you can find out more about gold value in another white paper.


The differences between carat and karat are easy to understand, just perhaps difficult to remember.

Remember that while the value of gold depends almost entirely on its karats, the number of carats in a diamond is just one of several factors determining the stone's quality and value.